Three-heat pad



Oct. l0, 1944.

E. c. TAYLOR THREE-HEAT PAD Filed June 6, 1942 /Bl H l l 73 ZZ L mw /2 /5/ 2 /3 /ff I INVENTOR ATTORN EYS Patented Oct. 10,

'mana-naar ran Edward C. Taylor, Longmeadow, Mass., assigner to William Bradford, Taunton, Mass.

Application June 6, 1942, Serial No. 446,019 z claims. (ci. 21a-4s) This invention relates to heating pads andparticularly to circuits therefor which make it pomble to maintain threeheats by means of a single thermostat.

In my prior Patent 2,237,852, April 8, 1941, I have shown a three-heat circuit of this general type which gives excellent separation of heats. and it has the additional advantage o! requiring only three conductors between the pad and the switch. It is found in practice that the use of more than three conductors is frequently undesirable, rendering the connecting cord too still. In certain cases, however, the use of a four-conductor cord is without objection and the present invention relates to a circuit adapted to a fourwire connecting rd and which has certain features of advantage in the way of simplicity and ease of obtaining any desired separation between the several temperatures at which the pad is intended to operate.

The invention willnow be described in connection with the accompanying drawing, in which Fig. 1 shows a plan view ofv a heating pad embodying the invention with the fabric covering broken away to show the overlying asbestos covered heating coil; and y 4 Fig. 2 is a diagram of the circuit.

Sewed or otherwise secured to the pad body I0 is an asbestos covered cord having a resistance wire I2 embedded therein. One end of the resistance wire is connected to a thermostat I3 by a exible lead I4, the other end of the thermostat being connected by a exible lead I5 to one of the wires I6 in the cord I1 which leads to the switch I8. As indicated in Fig. 1 this wire I6 passes through the switch without making any connection therein. The thermostat I3 is simply a safety device and ordinarily takes no part in the determination oi.' temperatures. The other end of the heating coil I2 is connected by a ilexible lead I8 to a heat control thermostat 20. A flexible lead 2| from the other end of this thermostat is connected to a wire 22 leading to the contact point ^H of the switch I8. Extending from the contact point M of the switch is a lead 23 extending to the approximate mid-point of tanthe thermostat 20, and through the coil I2. In this position the thermostat is subjected to the heat of coil I2 only, and not until this coil has reached this temperature (generally 180) for which. the thermostat is set is the circuit broken. In the medium position current passes through the wire 28, the resistancel 24, the wire 2|, and the thermostat 20, and then through the coil I2. The-resistance 24 (like the resistance 25) is positioned in heat transferring relation to the thermostat 20 so that the latter will be faster than the body of the coil. This will result in the circuit being broken before the coil I2 has reached the temperature for which the thermostat is adjusted. A similar effect but i'n a higher degree is obtained when the switch is set on the point L since in this case the current transverses both resistances 24 and 25.

It should be borne in mind that the resistances 24, 25 are much less in value than the coil I2 so that they do not produce a great change in the total resistance oi the circuit when they are dependent upon the individual resistances of the dem resistances 24 and .25. These two resistances v are connected to the wire 23 at their contiguous ends, and resistance 24 is connected to the wire 22 at 26. The second end of the resistance 25 resistance coils 24, 25. One set of values that has been found suitable for a voltage oi' 110 is 230 ohms for the coil I2 and 20 ohms each for the' stat-heating resistances 24, 25, will hel zero, 3.87

and 6.66 respectively. Since the medium and low heats are dependent upon the wattage dissipated in the thermostat-heating resistances it will be apparent that with the use of but a single thermostat the low and medium temperatures can be lsecured as desired merely by changinglthe values of the two resistances 24 and l25, as by varying their lengths until the correct value is obtained.

Subsequent pads can be made from the same dimensions and will give the same spacing of heats. f

What I claim is:

1. A three-heat pad comprising `a heating coil,

a thermostat embedded in the pad and in seriesy therewith, a pair oi resistances-in heat transferring adjacency to the thermostat, a four-wire conductor running from said pad, switch means in said conductor for connecting neither, one, or both o1 said resistances in' series with the heating coil.

2. A three-heat pad comprising a heating coil, a-

thermostat embedded in the pad and in series therewith, a pair of tandem resistances, one end of the tandem being connected to the side of the 

